The present application is the national stage under 35 U.S.C. 371 of international application PCT/SE00/00783, filed Apr. 26, 2000 which designated the United States, and which international application was published under PCT Article 21(2) in the English language.
This invention relates to storage of hazardous materials, especially low-level radioactive materials and chemical or biological hazardous materials. More particularly, the invention relates to a container for storing such materials, whether waste or useful materials, in a sealed storage space and a method for fluid-tight enclosure of the hazardous materials in a container body of concrete.
Prior art techniques for containing radioactive materials, such as fuel elements for nuclear reactors, include enclosing the materials in a shipping or storage container of reinforced concrete (DE-A-35 15 871). The radioactive material is introduced in a generally cylindrical monolithic container body with a vertically elongate storage space and an access opening connecting the storage space with the exterior surface of the container body at one end thereof. Apart from this opening the storage space is jointless.
After the radioactive material has been introduced in the storage space through the access opening, a pre-cast concrete closure body is placed in the access opening and bolted to the container body. A sealing member positioned in the gap between the wall of the access opening and the closure body ensures that the containment of the radioactive material will be fluid-tight.
In this prior art shipping and storage container, the sealing member is a factor of uncertainty. Although the sealing member may initially provide an adequate sealing, it may in the course of time lose some or all of its sealing ability, e.g. under the influence of the stored material.
An object of the invention is to ensure in a concrete container for storing a hazardous material a satisfactory containment of the material for a very long time, such as several decades.
In the container and the method according to the invention, the features of which are set forth in the claims, this object is achieved by casting concrete in an access opening of a container body after the introduction of the hazardous material in a storage space formed by the container body through the access opening and allowing the concrete to harden while supplying heat to the portion of the container body which surrounds the access opening. The supply of heat will cause the access opening to be expanded as a result of the thermal expansion of the heated portion of the container body. After a suitable heating period, the heated portion is allowed to assume the ambient temperature and thereby provide a shrink fit with the closure body formed by the hardened concrete cast in the access opening.
The shrink fit will be particularly effective if the container body comprises a metal reinforcement, preferably a prestressed reinforcement, extending about the access opening and this reinforcement is heated together with the concrete.
Preferably, the heating is accomplished by a heater, e.g. an electric heater, embedded in the concrete and extending about the access opening.